Since its discovery, HIV-1 has caused the death of 35 million people, and 36.9 million are living infected. Although researches have led to the development of antiretroviral therapies, which not only improve life expectation but also life quality of infected individuals, these therapies are not capable of eradicating the virus, and unfortunately there is no vaccine. The pathogenesis of HIV-1 is linked to a dysfunction of CD4 T cells that favors progression to AIDS. Therefore, given that most vaccines are based on T cell-dependent antibody production, the first part of my PhD research is devoted to understanding the impact of HIV-1 on CD4 T Follicular helper (Tfh) cells, which are essential for B cell activation and the production of specific antibodies. These cells are particularly crucial in the spleen, which is the major organ for B cell response. In the second part, I have analyzed the dynamics of memory CD4 T, Tfh and of B cells in mesenteric lymph nodes: an inductive site of the immune response that provides memory cells to the lamina propria (effector site) of the intestinal mucosa. Given the difficulties to study these deep organs, particularly during the acute phase in humans, I have used rhesus macaques infected with the simian immunodeficiency virus (SIV) to study the dynamics of Tfh cells. My results show an early depletion of splenic Tfh cells during the acute phase; a depletion that persists during the chronic phase within macaques in which the infection rapidly progresses to AIDS. Concomitantly, we report a depletion of memory B cells and low titers of anti-SIV IgG titers in these macaques. Furthermore, I observed a massive depletion of memory CD4 T, Tfh and B cells in mesenteric lymph nodes, as well as a phenotypic change of Tfh cells that become central memory cells associated with the upregulation of the expression of CD127 (IL-7 receptor). My results also show that environmental cytokines such as IL-7 and IL-27 contribute to their dysfunction as support the expression of transcription factors that inhibit Tfh cells such as T-bet, Foxo1 and Stat5. In conclusion, my results provide a better understanding of B cell dysfunction related to the early loss of the Tfh cells during HIV/SIV infection. Moreover, I hypothesize that the loss of immunity in the intestinal mucosa is due to the sudden depletion of memory CD4 T, Tfh and B cells in the mesenteric lymph nodes. Therefore, maintaining Tfh and memory CD4 T cells during the early phase of infection could be a promising therapeutic and vaccine approach for neutralizing HIV/SIV, as well as preventing bacterial translocation.